Combined production of heat and power provides the best energetic consumption of primary fuel energy. The consequence is longterm best economic results. Heat production in Ljubljana is for this reason based on such a system of primary fuel consu mption . Peak heat load and potential breakdowns of basic production sources are covered by cheap hot-water and steam boilers built in Toplarna Siska and on the location of Termoelektrarna - toplarna Ljubljana. The selected combination of production sources enables most rational heat production. The comparison of traditional ways of separate heat production and electric power and combined production of both sorts of energy is shown in the figure below. The fuel yield can thus be increased by 34 percent.